Frustrated magnets are a class of materials that should be magnetic at low temperatures but are not. In such materials, the geometric arrangement of the atoms prevents the spins of neighboring electrons from properly aligning with one another. This inability also leads to a large number of spin arrangements with nearly the same energy. Lifting this degeneracy can lead to unusual phenomena and unconventional magnetic states such as quantum spin liquids, an exotic state of matter consisting of disordered yet correlated electron spins. Rare-earth pyrochlore magnets have proven to be ideal materials for studying this physics. When these minerals have certain rare-earth ions, the energy degeneracy can be removed by defects, local deformations, and strains, which introduce an element of disorder. We use neutron scattering experiments to characterize the disorder in one of these minerals, and we analyze the underlying physics.

Specifically, we study the pyrochlore magnet ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. Our experiments show that random local deformations, by virtue of the magnetoelastic interaction, compete with the bare magnetic interactions and promote the rise of a spin liquid phase. This provides a very likely and qualitative explanation for a number of experimental features reported in this material, such as the lack of long-range order, the temperature dependence of the specific heat, and the energy broadening of the spin-excitations spectrum observed by neutron scattering. Finally, we discuss this work in the context of other studies that pointed out the role of disorder, and we suggest experiments on other similar quantum spin-ice candidates such as ${\mathrm{Pr}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7$, ${\mathrm{Pr}}_2{Hf}_2{\mathrm{O}}_7$, and ${\mathrm{Tb}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$.

This work deepens our understanding of quantum spin liquids, offering an original route to creating this exotic state of matter.